Machine for surfacing sheets of zinc and copper



Oct. 1, 1940.

T. J. MAssE MACHINE FOR SURFACING SHEETS 0F ZINC AND dOPPEB 2 Sheets-Sheet l Filed March 29, 1937 "r. J. MASSE 2,216,538

MACHINEYFOR SURFACING SHEETS 0F ZINC AND COPPER Oct. 1, 1940.

Filed March 29, 1937 2 Sheets-Sheet 2 Patented Oct. 1, 1940 PATENT OFFICE MACHINE FOR SURFACING SHEETS OF ZINC AND COPPER- Thomas Jerome Masse, Alexandria, near Sydney, New South Wales, Australia, assignor to The Edes Manufacturing Company,

Plymouth,

Mass, a corporation of Massachusetts Application March 29, 19.37, Serial No. 133,740

In Australia May 12, 1936 12 Claims.

This invention relates to new and useful apparatus for producing true surfaces on sheets of metal or the like. It provides apparatus of particular value for the manufacture of engravers sheets of zinc, copper or the like, having thicknesses that are highly uniform throughout the area of the sheets.

The object of this invention is .to enable production commercially and economically of sheets of zinc and copper (whether pure or alloyed with minor proportions of other metals) conforming to high standards of accuracy in thickness, flatness and finish such as are demanded .by photo-process etchers. In the present practice in the art these metal sheets must be subjected to costly and protracted grinding down, smooth grinding, and polish-ing, resulting in slow and costly production. It is impossible, when using the usual manufacturing practices, regularly to produce engraving sheets having a uniform gauge or thickness meeting the desires of the printing trade for printing work of high quality. However finely polished and uniform the sheets may appear to be, a great preponderance of the finished sheets vary in gauge to such an extent that an important part of the printers job, for example when making high quality printing matter from half-tone engraving, resides in lining up the engraved sheets on the printing presses, by cut-and-try methods, so that the tops of the sheets will be in reasonably accurate registration. It frequently requires as much as five or six hours to line up the engraved sheets on the printing press in making the press ready for operation. A variation of a few ten-thousandths of an inch in the level of the printing surface results in objectionable irregularities in the weight or appearance of the printed image.

Openating, however, with the process and machine hereinafter described, production of zinc sheets and copper sheets having commercially perfect surfaces for photo-engraving and like uses, and uniform in thickness, is effected rapidly at low cost and with minimum handling during production.

In the usual method of manufacturing engravers sheets, a cast stab of zinc or copper is annealed and is then rolled down in a succession of stages to produce plates about in thickness. Faults in the slab surface are accentuated in this rolling operation; hence the slabs must be cast in such a way as to produce good surfaces on them. The edges of the rolled plates are trimmed, then the plates are re-annealed, and they are then reduced in thickness by rolling in another mill.

It is a practical impossibility in this rolling operation to attain even texture throughout the sheets, or .to ensure the required accuracy in their thickness or to avoid producing surface spots or streaks by elongation of pit holes or other structuraPirregularities. Irregularlty in thickness of the sheets is largely due to the fact that a uniform temperature condition cannot be held throughout the sheets during the rolling. Given a certain pressure on the rolls, the bite will vary according to the hardness of the sheet, and the bite varies according to the temperature of the sheet, and this temperature is rarely, if ever, uniform'over the whole area of the sheet throughout a pass. After rolling, the sheets are subjected to a grinding operation in which the sheet surface is cut down, thus to remove surface defects, and to expose the sub-surface metal. As, however, grinding pads have a certain flexibility and nonuniformity, any inequality in thickness in the sheet is not corrected in the grinding operation, and assurance of -a truly'plane surface and uniformity in sheet thickness is not obtained. If there are differences in thickness at various parts of the sheet, or if there is any wave defect in the sheet, the excess thickness or the wave is not so far removed in the grinding as to make the sheet surface accurately plane and quite uniform in texture, and the thickness of the sheet is not brought to uniformity.

Considerable skill is required in the grinding operation to bring the sheets to within a permitted thickness tolerance and to produce a surface not marred by defects. Where the surface defects are such that a considerable depth of metal must be removed in the grinding to clear them, coarse grinding powder must be used, and then a finish grinding with finer material becomes necessary to remove scratches and roughnesses which are left in the coarse grinding step. Moreover, the grinding powder cannot be applied to the sheet uniformly, so that some portions of the sheet, where more powder is applied, are subjected to more intense grinding than others, and thus new surface and thickness irregularities are de veloped. Even with extreme care exercised in the grinding operations, the sheets are rarely finished quite flat and made even in thickness, and pits and dents frequently remain in the surface of the sheets. To reduce these last mentioned defects, tapping-up of the metal'during grinding is commonly resorted to, with the risk that the presence of tapping-up marks may affect the trade value of the sheet. Furthermore, it is impracticable to grind and finish every sheet objectionable range. And sheets within an acceptable thickness tolerance are not always uniform in thickness over their whole area.

In the method of the present invention, substantially perfect flatness is attained and substantially perfect finishing is also attained, together with assurance of uniform thickness over the whole area of the sheets well within the range of acceptable tolerance.

The present invention results, inter alia, in the following additional advantages:

(1) The slab casting operation is rendered economical because no'particular attention is necessary as heretofore in order to obtain a good surface on the slab. The casting temperature may be controlled for the production of slabs having a fine crystalline structure below the skin metal, irrespective of surface quality in the slab.

(2) Rolling is accomplished economically and rapidly because the sheets come off the mill slightly thicker all over than the thickness required in the finished sheet, and not necessarily uniformly thick in all places, the surplus thickness being sufficient to allow for the removal ofmetal in the machining operation.

(3) The rolling need not be effected in a mill designed and operated for production of good surfaced sheets, because inaccuracies in the rolled sheet surfaces are cut right away in a machining operation, leaving clean. fine-grained unbroken sub-surface metal exposed ready for polishing after superficial light grinding.

According to this new method for surfacing sheets, particularly engravers sheets of zinc, copper and the like, a rolled or otherwise worked sheet of a thickness somewhat in excess of the desired thickness'is placed and held securely on a trued upper surface of a carriage that is movable in a fixed linear path, with an entire face of the sheet exposed above this surface. A cutting diamond is repeatedly moved across the sheet at very high speeds and in a fixed circular path which is established so that the cutting tip of the diamond traverses the breadth of the entire sheet in a minor circular arc lying truly parallel to the trued upper surface of the carriage at a level below the exposed face of the sheet thereon. In the preferred embodiments, the carriage surface is slightly concave in transverse direction; and the axis of the cutting tool, or tools, is slightly tilted, so that the required true parallelism between the tool path and the carriage surface is constantly maintained. The diamond is preferably moved at a speed of-at leastseveral thousand feet per minute. Simultaneously with the revolution of the diamond, the carriage. is moved linearly in its fixed path at a regular speed, and the sheet held thereon is thus carried lngitudinally through the cutting path of the "amond The speed of movement of the carriage is correlated with the period of the diamond cycles so that successive swaths of the diamond overlap. Thus the entire breadth and length of the sheet are traversed by the swath of the diamond, with the diamond and the sheet always travelling in precisely fixed paths.

This method, in practice, continuously produces zinc and copper engravers sheets having a uniformity of gauge that never before has been obtainable by any regular or commercial method of production. After a sheet has been surfaced according to this method, the sheet is released and removed from its carriage. Microscopic surface irregularities remaining on the sheet, in the form of minute ridge marks between adjacent swaths of the cutting tool, may then be erased by light polishing and grinding operations, after which the sheets areready for sale or use for photo-engraving.

The new apparatus disclosed in this applica tion embodies novel constructions and arrangements adapted specially for the practice of the surfacing method described above. A slide carriage having a trued upper surface for supporting one or more unfinished sheets is provided, together with a trued supporting bed and means for moving the carriage at a regular speed on this bed. A cutting tool, or a plurality of tools, are located above the carriage, and means are provided for moving the cutting tools at very high speeds in a fixed circular path extending beyond opposite sides of a metal sheet to be surfaced. For example, each of the cutting tools is fastened securely to a carrier, such as a heavy disc or T piece, that is secured to a high speed spindle. The spindle is mounted for high speed revolution in a rigid supporting head overhanging the carriage, the headbeing secured to a massive framework, and means are provided for revolving the spindle to impart linear speeds of at least several thousand feet per minute to the cutting tools. The spindle is mounted in its head in such manner that each cutting tool remains constantly in its fixed circular path during operation, and the parts are arranged and set in relation to the trued surface of the carriage so that the tip of the tool, in-passing through a portion of its path, travels in a minor circular arcparallel to the trued surface of the carriage and at a level below the exposed face of a sheet held thereon.

A special feature of preferred embodiments of the invention resides in the construction of the carriage surface and the arrangement of the tool spindle in relation thereto, such that the circular path of movement of each cutting tool includes a minor circular arc lying parallel with the trued surface of the carriage and below the exposed face of a sheet held thereon, while the remainder of the path of the tool includes a major circular are lying above the exposed face of the sheet. According to this preferred embodiment the trued surface of the carriage, in longitudinal direction, is made straight and parallel with the path of carriage movement, but in transverse direction the surface is formed concavely with-a curvature that is uniform and circular in right transverse cross section. Thus the surface constitutes a section of a true cylinder. The cutting tool for cooperation with a sheet held on this surface is carried by a tilted spindle, the axis of revolution of the cutting tool intersecting theaxis of the curved surface and lying in a common straight plane therewith. This novel arrangement is of particular advantage in the surfacing of sheets for the reason that it eliminates any backward swath of the cutting tool over a finished portion of the sheet, thus avoiding danger of marring the sheet, and it also enables a substantial reduction in the length of the carriage and reduces the time required for a complete surfacing operation.

Another important feature resides in the use of a cutting diamond in a machine of the type described. I have found that a diamond tool is by far the most practical tool for the present purposes and that sheets of zinc, copper and other metals. may be surfaced continually over periods of several months without appreciable deterioration of the diamond or substantial variation in the quality of the finished sheets. The diamond sheds freely the metal chips swept off the face of the sheet, whereas other hard materials available for metal cutting either combine with the zinc or copper and will not shed the chips, or break down under the severe conditions of operation of the new method and apparatus and fail to produce a satisfactory product.

A further feature of preferred embodiments of the invention consists in the provision of two cutting tools which are secured in spaced relation, preferably at diametrically opposed points, on the revolving disc or T forming the tool carrier. Both tools are set to revolve in circular paths, and the tip of one of the tools may be located at a level very slightly lower than the tip of the other tool. In this way, one of the cutting tools removes most of the metal to be cut from the unfinished sheet in its swath, and the other tool following in the same or a closely spaced path acts as a finishing tool and removes to a considerable extent the strain-hardened metal surface left by the swath of the first tool. In practice, it has been found that the final grinding and polishing operations required to obtain a perfectly smooth sheet after treatment on thegsurfacing machine are considerably greater when a single cutting tool is used than when a pair of cutting tools is used as described.

Further features and advantages of my new method and apparatus will become apparent from the ensuing description when considered in connection with the accompanying drawings, which illustrate an embodiment of apparatus constructed in accordance with the invention.

In the drawings- Fig. 1 is a top plan of the machine;

Fig. 2 is a fragmentary side elevation view indicating in exaggerated way the tilting of the axis of the cutter head with respect to the surface of the carriage; 1

Fig. 3 is also an exaggerated view indicating the transverse curvature in the carriage surface which corresponds with the sweep of the cutter tool caused by the tilting of the axis of the cutter head;

Fig. 4. is a vertical transverse section through. the machine; and

Figs. 5, 6, 7 and 8 are detail views of an enlarged scale indicating the shape of the diamond cutter, its mounting in a tool holder by clamp or by cementing, and the setting of the tool holder adjustably for vertical position in a socket in the cutter head.

Referring to the drawings for illustrative details of construction, ID are the runways on the understructure H, and I2 is the carriage. I3 is a massive arm fixed to and overhanging the understructure The heavy spindle 4 is mounted in vertical bearings in the arm I 3. I5 is the tool head or disc foot on the bottom end of the spindle, and I6 is a belt pulley keyed to the upper part of the spindle. V II are the tool bracket pieces on the head l5. I8 is a zinc or copper sheet set on the surface of the carriage l2. The carriage I2 is traversable by means of the lead screw 2|. 22 is-a cone pulley on the butt end of the lead screw 2|, and 23 is a belt by which the lead screw pulley 22 is driven. 20 are lubricators inset in the carriage for distributing lubrication on the runways Ill. The spindle M is drawn up in its bearings by the compression collar spring 24 to ensure that it will run with its bottom end thrust flange 25 in close contact with the foot of the bottom bearing 36. The load is carried on the spring 24, the spring supporting washers being locked in position by the collar nuts 28, and

. lent mechanical device.

the downward thrust is taken on the thrust ball bearing 29. Both bearings are provided with oil thrower flanges 26 shrouded in annular gutter ways 21. 31 are holes in the carriage drilled into the cell 35 within it. This cell is connected by a flexible pipe 30 to the vacuum tank of a vacuum pump.

The machine is designed on massive lines in order to minimize the risk of vibration by which accuracy and fineness of the tool cut might be affected.

The diamond cutter 3| is mounted in the bottom end of the tool holder 32, and the tool holder is clamped by screws I!) in a split socket l1 and is adjusted in vertical direction by a micrometer backing screw 33 which is tapped through a bracket piece 34 fixed to the tool head I5 above the socket IT. The tool head I5 is preferably a heavy disc, but it might be in the shape of a T piece. It is extremely important that it be dy namically balanced accurately and the bearings fitted with great accuracy in order to diminish vibration. There may be either one or two tools fitted in the tool head. The fitting of the diamond cutter in the tool holder end is illustrated in Figs. 6 and 7.

The drawings do not show the transverse concaving of the carriage surface in Fig. 4. The exaggerated diagram Fig. 3 shows this concaving. The diameter of the swath of the diamond cutter must be greater than the width of the sheet l8 which is being machined so that a full width cut from edge to'edge of the sheet will be obtained. It is of great importance that the suction holes 31 shall be near to but not too close to the edges of the sheet in order that an effective holding down of the whole area of the sheet on the carriage surface shall be ensured without causing tendency to clouting or chattering of the tool on the sheet edges.

The diamond cutter is ground preferably to truncated pyramid shape with its face either turned or faceted as shown in Figs. 5, 6 and 7. As shown in Fig. '7 the diamond cutter is held in a recess in the toe of the tool holder by means of a clamp plate 3|a which is screwed onto the tool holder. In Figs. 5 and 6 the diamond cutter is cemented into a recess in the toe of the holder by means of a plastic cement such as is used by lapidaries. It is notable that either form of cutter is usable in the case of zinc sheets; in the case of copper sheets, however, the cemented setting may be necessary if the chip tends to crowd up against the end of the clamp plate (Fig. 7) and causes erosion of the metal. In Figs. 5, 6 and 7, the cutter face is raked about 7. This raking is not necessary; the cutter face is not required to have a rake in it. The diamond cutter appears to make its cuts quite satisfactorily even though its lip is more or less chipped.

The carriage I2 is traversed along the bed at a regular slow rate by the lead screw 2| or equiva- The carriage surface on which the sheet I8 is carried, and the carriage runners and the bed rails on which the carriage runs, must be finished quite accurately, and the runners and rails must be polished smooth. The cell 35 is cored in the body of the carriage l2 and the flexible pipe 30 and valves are fitted to connect this cell with a vacuum tank, which is associated with an air exhauster (not shown). The small holes 31 are drilled down through the sheetsupporting surface of the carriage, near its sides and ends, into this cell. These holes are in practice about an eighth of an inch in diameter; they are spaced apart about a quarter of an inch; and they are disposed so that when a sheet of standard area of zinc or copper, for whichthe machine is designed, is laid down on the carriage surface it will lap over the holes by an eighth of an inch to a quarter of an inch. Excessive overlap of the sheet edges may result in cockling of the sheet edge. With a vacuum of about 20 inches, a pressure of, approximately, 10 lbs. per square inch is applied to the sheet; that pressure is adequate for bringing and holding the under surface of the whole sheet into close contact with the true surface of the carrier. The sweep of the diamond cutter is true with respect to the carriage surface, and consequently the sheet is reduced in the machining operation to equal thickness on every part of it.

The spindle I4 is driven by a motor through a belt or otherwise at a speed determined to drive the diamond cutter at a linear speed of at least several thousand feet per minute.

Any tolerance differing (approximately) by more than one-half of one-thousandth of an inch in the thickness of the sheet after it has been cut down by the diamond tool is practically inadmissible; the depth of cut on well rolled sheets averages usually within two one-thousandths of an inch in the case of zinc, and about three onethousandths of an inch in the case of copper.

It has been determined in an exhaustive series of trials that no known material other than a diamond will serve satisfactorily for the cutter when surfacing engravers sheet of copper, zinc or the like. It is of importance that the tool holder shall be readily removable for inspection and replacement of the diamond with assurance of maintenance of exactness in its position so that the depth of cut shall not suifer any change when the holder has been removed and thereafter replaced in the socket in the revolving head. No cutting tool of-metal will produce a satisfactory result and stand up to the work for any useful period. Sapphire cutters do not hold their edge sufliciently long for practical purposes, although they will operate quite well though riskily for a rather limited time. The leading face may have a rake up to 6-8 degrees; the acuity of lip angle would thus be within a limit of 84-88 degrees.

The carriage is driven in slow progression during the rotation of the head, so that each successive diamond tool cut starts a small distance behind the preceding cut but overlaps it. Nevertheless, though the depth of cut is very small, a microscopic ridge is left between the successive cuts. Close observation shows that these ridges are produced under the heel of the cutter and not adjacent to the tool cut. These ridges should be erased by very light grinding in a separate operation after the surfaced sheet has been taken oil the carriage. The ridging between successive cuts is too minute for practical measurement, and is almost negligible, but even so, it is important to erase all ridges, however minute. Whatever imperfection is left in the surface of the sheets after the machining operation disappears in the light grinding and in the finish polishing operations.

If the carriage surface is quite flat the spindle axis must be accurately perpendicular to it. In that case the range of the carriage movement must be suflicient to enable the cutter to traverse the sheet twice, once in its forward sweep and once in its rearward swath. The rearward swath of the cutter is likely to mar the machined surface of the sheet. Moreover, the time required for the machining operation is consequently much greater than would be necessary if the machining operation were effected only in the forward sweep of the cutter, and in the latter case the dimensions of the machine could be correspondingly reduced. A second out has been proven to be quite unnecessary. In view of these facts the machine is preferably provided'with a carriage the surface of which is concaved in the transverse direction, as illustrated to an exaggerated extent in Figure 7, and with spindle bearings which are not in vertical relation to the line of movement of the carriage; these bearings are tilted forwardly in counter direction to the feed movement of the carriage, as illustrated to an exaggerated extent in Figure 8. The spindle is therefore off vertical sufllciently to tilt the cutter path, for example, about five one-thousandths of an inch. The carriage surface is concaved transversely in correspondence with the pitch of the cutter swath, this concaving being produced by machining the carriage with a surfacing tool carried in the machine's own tilted cutting head. The surface of the carriage is thus finished absolutely parallel with the dip in the cutter sweep. The sheets flex on the bed, setting down close on the carriage surface by reason of pneumatic suction between them and the carriage surface, which suction is obtained through perforations M by means of the vacuum pump (not shown) connected with chamber l5.

The sheet must be held absolutely inflexible and immovable on the carriage surface during the cutting operation. This is an essential condition of success in the operation. If any area of a sheet is loose on the carriage, chattering will occur and local inequality in thickness and surface irregularity will result. If the sheet were mechanically clamped to the carriage all around the clamps would be fouled by the cutter and chattering would occur in the middle area of the sheet, and no assurance would be provided for close seating of the sheet on the carriage surface. The pneumatic suction arrangement, however, ensures holding down of the sheet with the whole area of it contacting the carriage surface firmly and steadily. Mere opening of the air suction valve after the sheet is set in position on the carriage results in immediate secure holding down of the sheet over its whole area on the carriage surface. Mere reversal of the valve permits air release instantly and so frees the sheet for removal from the carriage.

Commercial success in the machining operation is referable to the high linear speed of the cutter, the very small depth of the cut, the constant maintenance of true parallelism. between the cutting path of the cutter and the carriage surface, the exposure of clean sub-surface metal for grinding and polishing, the utilisation of a diamond as the cutting tool, and the holding down of the sheet on the traversing carriage surface by pneumatic pressure during the machining operation. Extensive care in removing dust and excrescent material from the carriage surface and from the underside of the sheet is important. The depth of cut required for best results in the case of copper sheets is substantially more than the depth of out which is best in the case of zinc sheets.

' No attention is required from the operator during the machining operation; one operator can service a bank of machines in simultaneous operation. The diamond cutter shows negligible wear and it remains sharp for an indefinitely long time. Uniformity in thickness of the machined sheets does not vary during the life of thediamond, and accuracy in the machining operation does not depend on skill of the operator. Furthermore, the metal chips cut from the sheet are constantly piled at one point in condition for remelting, in contrast with present methods of grinding in which the metal removed from the sheets is scattered with the grinding pumice and is so contaminated by the latter that recovery is impractical.

It will be understood that the details of machine construction shown in the drawings and the special features of operating practice disclosed in the specification are presented only by way of illustration, and that departures from these are contemplated without departing from the contribution of the invention. It will also be evident that the invention may be used to great advantage for surfacing sheets in general to uniform thickness or gauge, without restriction to use in the manufacture of metal engravers sheets of copper, zinc, brass or the like.

What I claim as my invention and desire to secure by Letters Patent is:

1. A machine for surfacing zinc or copper sheets, comprising a trued horizontal bed, a carriage movable therealong; a true surface on said carriage' concaved in transverse direction but straight in longitudinal direction, a closely centered series of holes adjacent the four sides of the carriage surface and extending through the carriage surface into a cell within the carriage, a pipe connection from said cell to a vacuum pump, a bearing head overhanging the said bed above the carriage way, bearings in said head axially tilted in the direction of the carriage movement along the bed, a spindle fitted for rotation in said bearings at high speed, a tool holder carried in a head on said spindle and armed with a diamond cutter, said cutter positioned to cause its swaths to be truly parallel to the carriage surface and to overrlm the lines of holes adjacent the lateral sides of the carriage surface, and means for applying drive to the spindle and to the carriage at a complementary rate to procure overlap of the swaths of the diamond cutter.

2. A machine for surfacing sheets comprising, in combination, a carriage having a curved upper surface, longitudinal cross-sections of said surface being parallel lines and right transverse cross sections thereof being true circular arcs, means for moving said carriage in a fixed linear path parallel to the axis of said surface, a cutting tool, and means mounting said cutting tool for movement transversely across said surface in a fixed circular path including an are parallel to said surface, the radius of said circular arcs being 'much greater than the radius of said circular path.

3. A machine for surfacing sheets comprising, in combination, a carriage having a cylindrically concave upper surface uniform in right cross section, means for moving said carriage in a true straight path parallel to the axis of said surface, a cutting tool, and means mounting said cutting tool above said surface for revolution in a fixed circular path including an are parallel to said surface and about a fixed axis lying 'at an angle with respect to the axis of said surface and in a common straight plane therewith.

4. A machine for surfacing sheets to uniform thickness comprising a sheet holder movable in a fixed linear path, said sheet holder having a nearly fiat surface concave in transverse crosssection, a cutting diamond, and means mounting thickness said diamond for movement in a fixed circular path including a minor circular are lying parallel with the surface of said sheet holder and below the exposed face of a sheet thereon and including a major circular are lying above said face.

5. A machine for surfacing sheets to uniform thickness comprising a sheet holder movable in a fixed linear path, said sheet holder having a nearly fiat surface concave in transverse crosssection, a pair of spaced cutting diamonds, and means mounting said diamonds for movement in fixed circular paths each including a minor circular are lying parallel with the surface of said sheet holder and below the exposed face of a sheet thereon and each including a major circular are lying above said face.

6. A machine for surfacing engravers sheets of zinc, copper and the like to uniform thickness comprising a sheet holder movable in a fixed linear path, said sheet holder having a nearly fiat surface concave in transverse cross-section, a cutting diamond, means mounting said diamond for movement in a fixed circular path including a minor circular arc lying parallel with the surface of said sheet holder and below the exposed face of a sheet thereon and including a major circular are lying above said face, means for revolving said diamond at a speed of at least several thousand feet per minute, and means for moving said sheet holder in its path at a speed such that successive cutting swaths of the diamond overlap.

7. A machine for surfacing sheets to uniform comprising a carriage having a trued surface for supporting a sheet to be surfaced, said surface being straight in longitudinal direction and at most slightly concave in transverse direction, means for securely holding the sheet in contact with said surface of thecarriage with one face of the sheet entirely exposed, a

trued bed for the carriage, means mounting the carriage for longitudinal movement in a fixed straight path on said bed, a cutting tool, means for repeatedly sweeping said cutting tool at high speed entirely across a sheet on said carriage and in a fixed path extending truly parallel to said surface and transversely with respect to the path of movement of the sheet, and means for moving said carriage in its path, and for therewith moving the sheet through the path of said cutting tool, at a speed such that successive swaths of the cutting tool overlap.

8. A machine for surfacing sheets to uniform thickness comprising a carriage having a trued upper surface for supporting a sheet to be surfaced, said surface being straight in longitudinal direction and at most slightly concave in transverse direction, pneumatic means communicating with said surface for securely holding substantially the entire area of a sheet in contact therewith with one face of the sheet entirely exposed, a trued bed for the carriage including a plurality of precisely-aligned spaced runways, means mounting said carriage for longitudinal movement on said runways in a fixed straight path, a cutting tool, means for repeatedly sweeping said cutting tool at high speeds entirely across a sheet on said surface and in a fixed path extending truly parallel to said surface and transversely with respect to the path of movement of the sheet, and means for moving said carriage in its path, and for therewith moving the sheet through the path of said cutting tool, at a speed such that successive swaths of the cutting tool overlap.

9. A machine for surfacing sheets to uniform thickness comprising a carriage having a trued upper surface for supporting a sheet to be Surfaced, said surface being straight in longitudinal direction and at most slightly concave in transverse direction, means mounting said carriage for longitudinal movement in a fixed straight path, means for holding the sheet in contact with said surface with one face of the sheet entirely exposed, a rigid spindle head overhanging said carriage, a rotatable spindle mounted in said head about an axis intersectingsaid trued surface, means for revolving said spindle at high speeds, a cutting tool carrier secured to the spindle adjacent its lower end, a cutting tool securely mounted on and projecting downward from said carrier for rotation in a fixed circular path including a minor circular arc truly parallel to said surface and of a diameter greater than the breadth of the sheet, means for adjusting the position of said cutting tool so that its path will extend below the exposed face of a sheet supported on said trued surface, and means for moving said carriage in its path, and for therewith moving the sheet through the path of said cutting tool, at a speed such that successive swaths of the cutting tool overlap.

10. A machine for surfacing sheets to uniform thickness comprising a carriage having a trued upper surface for supporting a sheet to be surfaced, said surface being straight in longitudinal direction and at most slightly concave in transverse direction, means mounting said carriage for longitudinal movement in a fixed straight path, means for holding the sheet in contact with said surface with one face of the sheet entirely exposed, a rigid spindle head overhanging said carriage, a rotatable spindle mounted in said head and extending downward toward said surface, means for revolving said spindle at high speeds, a cutting tool carrier secured to the spindle adja cent its lower end, a pair of cutting tools securely mounted on said carrier in diametrically spaced relation-and projecting downward therefrom for rotation in fixed circular paths each including a minor circular arc truly parallel to said surface and of greater diameter than the breadth of the sheet, means for individually adjusting the positions of said cutting tools so that their paths will extend to accurately determined positions below the exposed face of a sheet supported on said surface, and means for moving said caniage in its path, and for therewith moving the sheet through the paths of said cutting tools, at a speed such that successive swaths of the cutting tools overlap.

11. The process for producing metal sheets and the like of highly uniform thickness which comprises revolving a cutting tool at a speed of at least several thousand feet per minute about a fixed axis inclined slightly from vertical, moving a carriage in a fixed linear path transverse to and through the lower portion of the tool path to machine the carriage surface and impart a transverse concavity thereto corresponding precisely to the cutting path of the tool thereafter ad- ,iusting the tool to space its cutting path from the carriage surface a distance corresponding to the desired thickness of the sheets, successively securing sheets having a thickness slightly greater than said desiredthickness onto the machined surface of the carriage so that the sheets are curved slightly to conform to said surface, and moving the carriage and each sheet thereon through the cutting path of the tool at a rate such that successive swaths of the tool overlap.

12. A machine for surfacing zinc or copper sheets, comprising a trued bed, a carriage movable horizontally therealong: a true plane surface on said carriage, a closely centred series of holes adjacent the four sides of the carriage and extending through the carriage surface into a cell within the carriage, a valved pipe connection from said cell to a vacuum pump, a bearing head overhanging the said bed above the carriage way, vertical hearings in said head, a spindle fitted for rotation in said bearings at high speed, a tool holder carried in a head on said spindle and armed with a diamond cutter, said cutter positioned to cause its swaths to be truly parallel to the carriage surface and to overrun the lines of holes adjacent the lateral sides of the carriage surface, and means for applying drive to the spindle and to the carriage at a complementary rate to procure overlap of the swaths of the diamond cutter.

THOMAS JEROME MASSE.

CERTIFICATE OF CORRECTION. Patent No. 2,216, 58. October 1, 191w. moms JEROME msss.

It is hereby certified thaterror appears in the printed specificationof the above numbered patent requiring correction as follows: Page 3, first column, line 147, for the word "of" read --on-- and second column, line 50, after "cutter" insert "settingpage 5, second column, lines 2, 15 and 214., claims 14., 5 and 6 respectively, afterlying"' insert 1 1lv--; page 6, first column, lines 12 and59, claims 9and 1.0 respectively, after "carrier" insert -rigidly--; and second column, line 7, claim 11, for "The" before "process" read -A-;'and that the said Letters Patent should be read with this correction therein that the same may conform to the record. of the case in the Patent Office.

Signed and sealed this 5th day of November, A. D. 1914.0.

4 Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

